Determination of Protein Phosphorylation Helps Diagnose Blood Cancers

Determination of protein phosphorylation in blood or minute tissue specimens might replace biopsies for cancer diagnosis and response to treatment.

Scientists used a system capable of analyzing whether individual cancer-associated proteins were present in a drop of blood or minute tissue specimens and whether modifications of the proteins varied in response to cancer treatments. The study focused on blood cancers, but the technique might also provide a faster, less invasive way to track solid tumors.

The Cell Biosciences (Palo Alto, CA, USA) protein analysis system used in the study is an ultrasensitive nanofluidic immunoassay system designed to analyze extremely small biological samples. Traditional protein analysis techniques can require as many as 100,000 cells, which complicates protein analysis in limited samples. The Cell Biosciences system can measure cell-signaling proteins reproducibly in as few as 25 cells.

Stanford Medical School (Palo Alto, CA, USA) investigators collaborated with scientists from Cell Biosciences to separate cancer-associated proteins in narrow capillary tubes based on their charge, which varies according to modifications on the proteins' surface. Two versions of the same protein, one phosphorylated and one not, were easily distinguished because they traveled different distances in the tube. Antibodies were than used to identify the relative amounts and positions of the various proteins.

Variations in the way a protein is modified, or phosphorylated, can affect how it functions in tumor progression. Cancer cells often evade common therapies by altering their levels of protein expression and degrees of phosphorylation. Analyzing repeated small samples from a tumor undergoing treatment might allow doctors to head off rogue cells before they have a chance to proliferate into a more resistant tumor or to identify patients likely to fail standard approaches to treatment.

Alice Fan, M.D., a clinical instructor in the division of oncology at the Stanford medical school performed the study in the laboratory of Dean Felsher, MD, PhD, associate professor of medicine and of pathology and the leader of the Stanford molecular therapeutics program. "This technology allows us to analyze cancer-associated proteins on a very small scale," said Professor Felsher, a member of Stanford's Cancer Center, who studies how cancer genes called oncogenes initiate and influence tumor progression in many types of cancers. "Not only can we detect picogram levels--one-trillionth of a gram--of protein, but we can also see very subtle changes in the ways the protein is modified."

The study was reported in the advance online issue of the journal Nature Medicine on April 12, 2009.

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